%META:TOPICPARENT{name="VOSIndex"}%

---+ Guide to using SPARQL inside XSLT

This guide demonstrates how Virtuoso allows SPARQL queries to be embedded into 
an XSLT style sheet, and executed against a remote SPARQL endpoint (here, we use 
the [[http://lod.openlinksw.com/sparql/][LOD Cloud Cache]]) to retrieve data for 
use in HTML output. 

---++Implementation

   * The key component of this feature is the <code>&lt;xsl:for-each-row&gt;</code> 
control element. This element has one attribute, named either <code>"sparql"</code> 
or <code>"sql"</code>; the value of the attribute is an XPath expression that 
returns the text of the query to executed, e.g.,
<verbatim>
<xsl:for-each-row sparql="string(\044query)">
</verbatim>
   * The XPath expression can be a plain string constant, but because the query can 
be quite long, it is usually more convenient to store the text in a variable and 
refer to that variable.
   * The SPARQL query may contain parameters (written in the form <code>?:name</code>). 
A parameter of this sort will get its value from the XSLT variable <code>$name</code>. 
(If there is any nesting or recursion, the value(s) will come from the innermost 
variables.)
   * The query execution in turn creates new XSLT variables that exist inside the 
body of <code>&lt;xsl:for-each-row&gt;</code>. Each result column of a query becomes 
one XSLT variable. 
   * The body of <code>&lt;xsl:for-each-row&gt;</code> is instantiated once for each 
row of the query result set, with new values for the variables in each instantiation.


---++Example 

   1 Execute from iSQL:
<verbatim>
SQL>  xslt_sheet ('local://friends.xsl', 
                  xtree_doc ('<xsl:stylesheet xmlns:xsl = "http://www.w3.org/1999/XSL/Transform" version = "1.0" xmlns:sample="http://xslt/" >
                              <xsl:output method = "html" version="1.0" doctype-public="http://public" doctype-system="http://system" />
                              <xsl:param name="fname" select="''Kingsley''" />
                              <xsl:param name="lname" select="''Idehen''" />
                              <xsl:param name="fullname" select="''Kingsley Idehen''" />
                              <xsl:variable name = "query">
<![CDATA[
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
SELECT DISTINCT ?maxlinkg 
                ?fnick 
                ?ffullname 
                ?ffname 
                ?flname 
                ?fimg 
WHERE
  {
    SERVICE <http://lod.openlinksw.com/sparql/> (DEFINE lang:dialect 65535)
      {
        { SELECT DISTINCT                                                     ?maxlinkg 
                                                                              ?fg 
                                                                              ?fnick
                                                                              ?ffullname 
                          ?ffname (bif:__max_notnull (?flname1, ?flname2)) AS ?flname 
                                                                              ?fimg
          WHERE
            {
              { SELECT (MAX(?linkg)) AS ?maxlinkg 
                                        ?f 
                 WHERE
                   {
                     { SELECT DISTINCT ?k 
                        WHERE
                          { GRAPH ?kg 
                              {
                                { ?k  foaf:firstName   ?:fname  
                                   ;  foaf:familyName  ?:lname 
                                }
                                UNION
                                { ?k  foaf:firstName    ?:fname
                                   ;  foaf:family_name  ?:lname 
                                }
                                UNION
                                { ?k  foaf:name       ?:fullname } 
                          } 
                     } 
                   }
                 GRAPH ?linkg { ?k foaf:knows ?f } 
            } }
            GRAPH ?fg 
              {               ?f  a                 <http://xmlns.com/foaf/0.1/Person>
                .  OPTIONAL { ?f  foaf:firstName    ?ffname     }
                   OPTIONAL { ?f  foaf:nickname     ?fnick      }
                   OPTIONAL { ?f  foaf:name         ?ffullname  }
                   OPTIONAL { ?f  foaf:familyName   ?flname1    }
                   OPTIONAL { ?f  foaf:family_name  ?flname2    }
                   OPTIONAL { ?f  foaf:img          ?fimg       }
              }
            FILTER ( bound ( ?ffullname ) 
                     || ( bound ( ?ffname ) 
                          &amp;&amp; ( bound ( ?flname1 ) 
                                  || bound ( ?flname2 ) 
                           ) ) )
          } 
          ORDER BY ?fullname 
                   ?ffname 
        } 
      } 
  }
]]></xsl:variable>
<xsl:template match = "/">
  <html><head>Simple demo for SPARQL inside XSLT</head>
    <body>
    <p>Known friends of <xsl:choose>
         <xsl:when test="\044fullname"><xsl:value-of select="\044fullname" /></xsl:when>
         <xsl:otherwise><xsl:value-of select="\044fname" />&nbsp;<xsl:value-of select="\044lname" /></xsl:otherwise>
       </xsl:choose></p>
    <table>
    <xsl:for-each-row sparql="string(\044query)">
      <tr><td><xsl:if test="\044fimg"><a href="{\044fimg}" ><img src="{\044fimg}" width="64" height="64" /></a></xsl:if></td>
      <td><a href=".?fname={\044ffname}&lname={\044flname}&fullname={\044ffullname}">
      <b><xsl:choose>
         <xsl:when test="\044ffullname"><xsl:value-of select="\044ffullname" /></xsl:when>
         <xsl:otherwise><xsl:value-of select="\044ffname" />&nbsp;<xsl:value-of select="\044flname" /></xsl:otherwise>
       </xsl:choose></b></a><br />
       <xsl:if test="\044fnick">Nick: <xsl:value-of select="\044fnick" /><br /></xsl:if>
       (data from <a href="{\044maxlinkg}" ><xsl:value-of select="\044maxlinkg" /></a> <!-- and <a href="{\044maxfg}" ><xsl:value-of select="\044maxfg" /></a>-->)
       </td></tr>
    </xsl:for-each-row>
    </table>
    </body>
  </html>
</xsl:template>
</xsl:stylesheet>'));

DB.DBA.VHOST_DEFINE 
  ( lpath=>'/friends/', 
    ppath => '/!friends/', 
    is_dav => 1, 
    vsp_user => 'dba', 
    opts => vector('noinherit', 1)
  );

CREATE PROCEDURE WS.WS."/!friends/" 
  ( INOUT  path    VARCHAR, 
    INOUT  params  ANY, 
    INOUT  lines   ANY
  )
{
  http_value (xslt ('local://friends.xsl', xtree_doc ('<fake />'), params));
}
;

registry_set ('/!friends/', 'no_vsp_recompile')
;
</verbatim>
   1 Go to [[http://cname/friends/][http://cname/friends/]], where results should look something like this:
%BR%%BR%<img src="%ATTACHURLPATH%/xslt1.png" style="wikiautogen"/>%BR%%BR%
%BR%%BR%<img src="%ATTACHURLPATH%/xslt2.png" style="wikiautogen"/>%BR%%BR%